The present invention relates to new porcine circovirus (PCV for Porcine CircoVirus) strains responsible for the PMWS syndrome (Porcine Multisystemic Wasting Syndrome also called Post-Weaning Multisystemic Wasting Syndrome) to reagents and methods allowing their detection, to methods of vaccination and to vaccines, as well as to methods of producing these reagents and vaccines.
PCV was originally detected as a noncytopathogenic contaminant in pig kidney cell lines PK/15. This virus was classified among the Circoviridae with the chicken anaemia virus (CAV for Chicken Anaemia Virus) and the PBFDV virus (Pscittacine Beak and Feather Disease Virus). It is a small nonenveloped virus (from 15 to 24 nm) whose common characteristic is to contain a genome in the form of a circular single-stranded DNA of 1.76 to 2.31 kb. It was first thought that this genome encoded a polypeptide of about 30 kDa (Todd et al., Arch Virol 1991, 117; 129-135). Recent work has however shown a more complex transcription (Meehan B. M. et al., 1997, 78; 221-227). Moreover, no significant homologies in nucleotide sequence or in common antigenic determinants are known between the three types of circoviruses known.
The PCV derived from the PK/15 cells is considered not to be pathogenic. Its sequence is known from B. M. Meehan et al., J. Gen. Virol 1997 (78) 221-227. It is only very recently that some authors have thought that strains of PCV could be pathogenic and associated with the PMWS syndrome (Gupi P. S. Nayar et al., Can. Vet. J, vol. 38, 1997: 385-387 and Clark E. G., Proc. Am. Assoc. Swine Prac. 1997; 499-501). Nayar et al. have detected PCV DNA in pigs having the PMWS syndrome using PCR techniques. No wild-type PCV strain has however been isolated and purified so far.
The PMWS syndrome detected in Canada, the United States and France is clinically characterized by a gradual loss of weight and by manifestations such as tachypnea, dyspnea and jaundice. From the pathological point of view, it is manifested by lymphocytic or granulomateus infiltrations, lymphadenopathies and, more rarely, by hepatitis and lymphocytic or granulomateus nephritis (Clark E. G., Proc. Am. Assoc. Swine Prac. 1997; 499-501; La Semaine Vxc3xa9txc3xa9rinaire No. 26, supplement to La Semaine Vxc3xa9txc3xa9rinaire 1996 (834); La Semaine Vxc3xa9txc3xa9rinaire 1997 (857): 54; Gupi P. S. Nayar et al., Can. Vet. J, vol. 38, 1997; 385-387).
The applicant has succeeded in isolating five new PCV strains from pulmonary or ganglionic samples obtained from farms situated in Canada, the United States (California) and France (Brittany), hereinafter called circoviruses according to the invention. These viruses have been detected in lesions in pigs with the PMWS syndrome, but not in healthy pigs.
The applicant has, in addition, sequenced the genome of four of these strains, namely the strains obtained from Canada and the United States as well as two French strains. The strains exhibit a very strong homology with each other at the nucleotide level, exceeding 96% and much weaker with the PK/15 strain, about 76%. The new strains can thus be considered as being representative of a new type of porcine circovirus, called here type II, type I being represented by PK/15.
The subject of the present invention is therefore the group II porcine circovirus, as defined above, isolated or in the form of a purified preparation.
The invention relates to any porcine circovirus capable of being isolated from a physiological sample or from a tissue sample, especially lesions, from a diseased pig having the PMWS syndrome, especially following the method described in the examples, in particular type II circovirus.
The subject of the present invention is more particularly purified preparations of five strains, which were deposited at the ECACC (European Collection of Cell Cultures, Centre for Applied Microbiology and Research, Porton Down, Salisbury, Wiltshire SP4 0JG, United Kingdom) on Thursday Oct. 2, 1997:
provisional accession No. V97100219 (called here Imp. 1008PCV)
provisional accession No. V9700218 (called here Imp. 1010PCV)
provisional accession No. V97100217 (called here Imp. 999PCV), and, on Friday Jan. 16 1998:
provisional accession No. V98011608 (called here Imp. 1011-48285)
provisional accession No. V98011609 (called here Imp. 1011-48121).
The invention aims to consider the porcine circoviruses isolated from a diseased pig and/or the circoviruses having a significant serological similarity with the strains of the invention and/or the circoviruses having cross-hybridization with the strains of the invention under stringency conditions such that there is no hybridization with the PCV PK/15 strain.
The viral strains isolated from a physiological sample or from a tissue sample, especially a lesion, from a pig having the PMWS syndrome can be advantageously propagated on cell lines such as especially pig kidney cell lines, in particular PK/15 cells free from contamination (in particular for PCV, as well as for pestiviruses, porcine adenoviruses and porcine parvoviruses) for their multiplication or specifically for the production of antigen, whole (e.g. virus) and/or subunits (e.g. polypeptides).
Very remarkably and unexpectedly, these isolates have proved very productive in culture on PK/15 cells, which have undeniable advantages for the production of virus or antigen, in particular for the production of inactivated vaccine.
The subject of the present invention is also the preparations of circoviruses isolated after passages on cells, especially cell lines, e.g. PK/15 cells, cultured in vitro while being infected with at least one of the circoviruses according to the invention or of any porcine circovirus capable of being isolated form a physiological sample or from a tissue sample, especially lesions, from a pig having the PMWS syndrome. Its subject is also the culture extract or supernatant, optionally purified by standard techniques, and in general any antigenic preparation obtained from in vitro cultures.
The subject of the invention is also the immunogenic active ingredients and the vaccines containing at least one antigen as defined above.
They may be immunogenic active ingredients based on attenuated live whole viruses, or vaccines prepared with these active ingredients, the attenuation being carried out according to the customary methods, e.g. by passage on cells, preferably by passage on pig cells, especially lines, such as PK/15 cells (for example from 50 to 150, especially of the order of 100, passages). These vaccines comprise in general a vehicle or diluent acceptable from the veterinary point of view, optionally an adjuvant acceptable from the veterinary point of view, as well as optionally a freeze-drying stabilizer.
These vaccines will preferably comprise from 103 to 106 TCID50.
They may be immunogenic active ingredients or vaccines based on circovirus antigen according to the invention, in an inactivated state. The vaccine comprises, in addition, a vehicle or a diluent acceptable from the veterinary point of view, with optionally in addition an adjuvant acceptable from the veterinary point of view.
The circoviruses according to the invention, with the fractions which may be present, are inactivated according to techniques known to persons skilled in the art. The inactivation will be preferably carried out by the chemical route, e.g. by exposing the antigen to a chemical agent such as formaldehyde (formalin), paraformaldehyde, xcex2-propiolactone or ethyleneimine or its derivatives. The preferred method of inactivation will be herein the exposure to a chemical agent and in particular to ethyleneimine or to xcex2-propiolactone.
Preferably, the inactivated vaccines according to the invention will be supplemented with adjuvant, advantageously by being provided in the form of emulsions, for example water-in-oil or oil-in-water, according to techniques well known to persons skilled in the art. It will be possible for the adjuvant character to also come from the incorporation of a customary adjuvant compound into the active ingredient.
Among the adjuvants which may be used, there may be mentioned by way of example aluminium hydroxide, the saponines (e.g. Quillaja saponin or Quil A; see Vaccine Design, The Subunit and Adjuvant Approach, 1995, edited by Michael F. Powel and Mark J. Newman, Plennum Press, New-York and London, p.210), Avridine(copyright) (Vaccine Design p. 148), DDA (Dimethyldioctadecylammonium bromide, Vaccine Design p. 157), Polyphosphazene (Vaccine Design p. 204), or alternatively oil-in-water emulsions based on mineral oil, squalene (e.g. SPT emulsion, Vaccine Design p. 147), squalene (e.g. MF59, Vaccine Design p. 183), or water-in-oil emulsions based on metabolizable oil (preferably according to WO-A-94 20071) as well as the emulsions described in U.S. Pat. No. 5,422,109. It is also possible to choose combinations of adjuvants, for example Avridine(copyright) or DDA combined with an emulsion.
These vaccines will preferably comprise from 106 to 108 TCID50.
The live vaccine adjuvants can be selected from those given for the inactivated vaccine. The emulsions are preferred. To those indicated for the inactivated vaccine, there may be added those described in WO-A-9416681.
As freeze-drying stabilizer, there may be mentioned by way of example SPGA (Bovarnik et al., J. Bacteriology 59, 509, 950), carbohydrates such as sorbitol, mannitol, starch, sucrose, dextran or glucose, proteins such as albumin or casein, derivatives of these compounds, or buffers such as alkali metal phosphates.
The vaccines according to the invention may comprise one or more active ingredients (antigens) of one or more (2 or 3) of the circoviruses according to the invention.
The invention also provides for combining vaccination against the porcine circovirus with a vaccination against other pig pathogens, in particular those which can be associated with the PMWS syndrome. The vaccine according to the invention may therefore comprise another valency corresponding to another pig pathogen.
The applicant has, in addition, obtained the genome of four of the isolates, identified SEQ ID NO: 1 to 4 and optionally 6.
The subject of the present invention is therefore a DNA fragment containing all or part of one of these sequences. It goes without saying that the invention automatically covers the equivalent sequences, that is to say the sequences which do not change the functionality or the strain-specificity of the sequence described or of the polypeptides encoded by this sequence. There will of course be included the sequences differing by degeneracy of the code.
The invention also covers the equivalent sequences in the sense that they are capable of hybridizing with the above sequence under high stringency conditions and/or have a high homology with the strains of the invention and belong to group II defined above.
These sequences and their fragments can be advantageously used for the in vitro or in vivo expression of polypeptides with the aid of appropriate vectors.
In particular, the open reading frames, forming DNA fragments according to the invention, which can be used to this effect have been identified on the genomic sequence of the type II circoviruses. The invention relates to any polypeptide containing at least one of these open reading frames (corresponding amino acid sequence). Preferably, the invention relates to a protein essentially consisting of ORF4, ORF7, ORF10 or ORF13.
For the expression of subunits in vitro, as a means of expression, E. coli or a baculovirus will be preferably used (U.S. Pat. No. 4,745,051). The coding sequence(s) or their fragments are integrated into the baculovirus genome (e.g. the baculovirus Autographa californica Nuclear Polyhedrosis Virus AcNPV) and the latter is then propagated on insect cells, e.g. Spodoptera frugiperda Sf9 (deposit ATCC CRL 1711). The subunits can also be produced in eukaryotic cells such as yeasts (e.g. Saccharomyces cerevisiae) or mammalian cells (e.g. CHO, BHK).
The subject of the invention is also the polypeptides which will be produced in vitro by these expression means, and then optionally purified according to conventional techniques. Its subject is also a subunit vaccine comprising at least one polypeptide as thus obtained, or fragment, in a vehicle or diluent acceptable from the veterinary point of view and optionally an adjuvant acceptable from the veterinary point of view.
For the expression in vivo for the purpose of producing recombinant live vaccines, the coding sequence(s) or their fragments are inserted into an appropriate expression vector under conditions allowing the expression of the polypeptide(s). As appropriate vectors, there may be used live viruses, preferably capable of multiplying in pigs, nonpathogenic for pigs (naturally nonpathogenic or rendered as such), according to techniques well known to persons skilled in the art. There may be used in particular pig herpesviruses such as Aujeszky""s disease virus, porcine adenovirus, poxviruses, especially vaccinia virus, avipox virus, canarypox virus, swinepox virus. Plasmid DNAs can also be used as vectors (WO-A-90 11092, WO-A-93 19813, WO-A-94 21797, WO-A-95 20660).
The subject of the invention is therefore also the vectors and the recombinant live vaccines or plasmid vaccines (polynucleotide or DNA vaccines) thus prepared, the vaccines comprising, in addition, a vehicle or diluent acceptable from the veterinary point of view.
The subject of the present invention is also a method which makes it possible to induce an immune response in pigs towards circoviruses according to the invention. Its subject is in particular a method of vaccination which is effective in pigs.
This method provides for the administration to pigs, in one or more portions, of a vaccine above. It is also possible to combine several types of the above vaccines in the same vaccination protocol.
This method provides not only for administration to adult pigs, but also to young pigs or to pregnant females. The vaccination of the latter makes it possible to confer passive immunity to the newborns (maternal antibodies).
The invention also offers the possibility of diagnosing the presence of the circoviruses according to the invention in pigs. Its subject is therefore diagnostic tests and methods relating thereto using reagents which will be described below.
Knowledge of the sequences of the different circoviruses makes it possible to define common sequences which make it possible to produce reagents capable of recognizing all the porcine circoviruses known.
Persons skilled in the art will also be able to select fragments of the sequences corresponding to regions exhibiting little or no homology with the corresponding PK/15 circovirus sequence in order to carry out a specific diagnosis.
Sequence alignments make it possible for persons skilled in the art to select a reagent in accordance with their wishes.
A first reagent consists in the DNA sequences disclosed here and their fragments, which will in particular be used as probes or primers in well-known hybridization or PCR (Polymerase Chain Reaction) techniques.
A second reagent consists in the polypeptides encoded by these sequences from the virus or expressed with the aid of a vector (see above), or synthesized by the chemical route according to conventional techniques for peptide synthesis.
A third and fourth reagent consists in respectively polyclonal and monoclonal antibodies which may be produced according to the customary techniques from the virus, the polypeptides or fragments, extracted or encoded by the DNA sequences.
These second, third and fourth reagents may be used in a diagnostic method, a subject of the invention, in which a test is carried out, on a sample of physiological fluid (blood, plasma, serum and the like) or a sample of tissue (ganglia, liver, lungs, kidneys and the like) obtained from a pig to be tested, for the presence of an antigen specific for a circovirus according to the invention, by seeking to detect either the antigen itself, or antibodies directed against this antigen.
The antigens and antibodies according to the invention may be used in any known laboratory diagnostic technique.
However, it will be preferable to use them in techniques which can be used directly in the field by the veterinary doctor, the breeder or the owner of the animal. Persons skilled in the art have available a range of laboratory and field techniques and are therefore in the perfect position to adapt the use of this antigen and/or antibodies as diagnostic reagent(s).
The diagnostic techniques which will be preferably used within the framework of the present invention are Western blotting, immunofluoroescence, ELISA and immunochromatography.
As regards the use of immunochromatography methods, specialists can refer in particular to Robert F. Zurk et al., Clin. Chem. 31/7, 1144-1150 (1985) as well as to patents or patent applications WO-A-88/08 534, WO-A-91/12528, EP-A-291 176, EP-A-299 428, EP-A-291 194, EP-A-284 232, U.S. Pat. No. 5,120,643, U.S. Pat. No. 5,030,558, U.S. Pat. No. 5,266,497, U.S. Pat. No. 4,740,468, U.S. Pat. No. 5,266,497, U.S. Pat. No. 4,855,240, U.S. Pat. No. 5,451,504, U.S. Pat. No. 5,141,850, U.S. Pat. No. 5,232,835 and U.S. Pat. No. 5,238,652.
Accordingly, it is preferably sought to detect specific antibodies in the sample by an indirect test, by competition or by displacement. To do this, the antigen itself is used as diagnostic reagent, or a fragment of this antigen, conserving recognition of the antibodies. The labelling may be advantageously a labelling with peroxidase or a special labelling, preferably with colloidal gold.
It may also be desired to detect the antigen itself in the sample with the aid of a labelled antibody specific for this antigen. The labelling is advantageously as described above.
By antibody specific for the antigen which can be used in particular in competition or displacement or for the detection of the antigen itself, there is understood monoclonal or polyclonal antibodies specific for the antigen, fragments of these antibodies, preferably Fab or F(ab)xe2x80x22 fragments.
Another feature of the invention is the roduction of polyclonal or monoclonal antibodies specific for the antigen in accordance with the invention, it being possible for these antibodies to then be used in particular as diagnostic reagent for the detection of the antigen in a sample of physiological fluid or in a tissue sample, or even for the detection of antibodies present in such a sample or specimen. The invention also includes the immunologically functional fragments of these antibodies, in particular the F(ab) and F(ab)xe2x80x22 fragments.
Antibodies can be prepared by the customary techniques. Reference may be made in particular to Antibodies, A Laboratory Manual, 1988, Cold Spring Harbor Laboratory, USA or to J. W. Goding, Monoclonal Antibodies: Principles and Practice, Academic Press Inc., whose contents are incorporated herein by reference.
It will be possible in particular, as is known per se, to carry out the fusion of spleen cells of mice, immunized with the antigen or with at least one of its fragments, with suitable myelomatous cells.
The subject of the invention is also a preparation, preferably pure or partially pure, or even crude, of monoclonal or polyclonal antibodies specific for the antigen, especially mouse or rabbit antibodies.
The present invention also makes it possible to determine epitopes of interest especially on the basis of the DNA sequences described here, whether epitopes of vaccinal interest or epitopes of interest in diagnosis. From the DNA sequence of the genome of the circovirus according to the invention, persons skilled in the art are in a position to determine epitopes according to known methods, for example an appropriate computer program or PEPSCAN. Epitopes are immunodominant regions of proteins and are as such regions exposed at the surface of the proteins. They can therefore be recognized by antibodies and thus be particularly used in the field of diagnosis either for the preparation of antibodies for diagnostic purposes or for the production of corresponding peptides which can be used as diagnostic reagents.
At the very least, an epitope is a peptide having from 8 to 9 amino acids. A minimum of 13 to 25 amino acids is generally preferred.
Persons skilled in the art are therefore in a position, using one or more of these techniques as well as the other available techniques, to find epitopes for using peptides or antibodies for diagnostic purposes.
The subject of the invention is also a diagnostic kit comprising this antigen and/or polyclonal or monoclonal antibodies specific for this antigen. These are in particular diagnostic kits corresponding to the diagnostic techniques described above.